mvvmbasic.md

MVVM Basic

Notice: MVVM Basic has been superseded by the MVVM Toolkit and will be removed as an option in a future version of Template Studio.

A guide is available if you want to use the new MVVM Toolkit and are migrating from MvvmBasic.

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MVVM Basic is not a framework but provides the minimum functionality necessary to create an app using the Model-View-ViewModel (MVVM) pattern. It is unique to projects generated with Template Studio and was created for people who can't or don't want to use a 3rd party MVVM Framework such as MVVM Light or Prism.

MVVM Basic is not intended to be a fully featured MVVM Framework and does not include some features that other frameworks do as for example messaging.

MVVM Basic can also serve as a basis for developers who want to create their own MVVM implementation. By providing only the most basic of extra functionality but still following common conventions it should be the easiest option if you want to modify the generated code to meet your preferred way of working.

MVVM Basic uses the Microsoft.Extensions.Hosting NuGet Package as application host to provide configuration and dependency injection. For more information see .NET Generic Host documentation.

Core files

Projects created with MVVM Basic contain four important classes:

• Observable
• RelayCommand
• INavigationAware
• ApplicationHostService

Observable contains an implementation of the INotifyPropertyChanged interface and is used as a base class for all ViewModels. This makes it easy to update bound properties on the View.

RelayCommand contains an implementation of the ICommand interface and allows the View to call commands on the ViewModel, rather than handle UI events directly. You can see examples of RelayCommand in use in a generated project.

INavigationAware is an interface to be implemented on ViewModels. It provides you with the navigation events OnNavigatedTo and OnNavigatedFrom.

ApplicationHostService is the startup service of the app, it's created on App.xaml.cs file and handles the app initialization and the main window creation.

Working with dependency injection

MVVMBasic projects use dependency injection (DI) to register and consume object instances in the App (Views, ViewModels, Services, etc.).

All classes you want to use with DI must be registered in the ConfigureServices method of App.xaml.cs file.

private void ConfigureServices(HostBuilderContext context, IServiceCollection services)
{
    // Use singleton if you want to share the instance across your app
    services.AddSingleton<IMyService, MyService>();

    // Use transient if you want to obtain new instances
    services.AddTransient<IMyService, MyService>();
}

Once these services are registered you can retrieve instances in any class constructor, like for example a ViewModel.

public class MainViewModel : Observable
{
    private readonly INavigationService _navigationService;

    public MainViewModel(INavigationService navigationService)
    {
        _navigationService = navigationService;
    }
}

Navigation

MVVM Basic assumes ViewModel-based navigation. This means that a ViewModel will trigger navigation to another ViewModel. This should be done by calling the NavigateTo method on the INavigationService and passing the type full name of the page's view-model you wish to navigate to. In order to resolve the navigation, there is a 1 to 1 relationship between the page and view-model and it's configured in the PageService using the Configure method.

Page configuration code

Configure<MainViewModel, MainPage>();

ViewModel navigation code

_navigationService.NavigateTo(typeof(MainViewModel).FullName);

Reacting to navigation events

ViewModels can react to the navigation events implementing the INavigationAware and use the OnNavigatedTo to initialize data (i.e. SettingsViewModel). On this method, you can also read the navigation parameter.

public void OnNavigatedTo(object parameter)
{
    VersionDescription = $"AppName - {_applicationInfoService.GetVersion()}";
    Theme = _themeSelectorService.GetCurrentTheme();
}